1. Field of the Invention
This invention relates to internal combustion of fuel/oxidizer mixtures, and more particularly to the injection of nanostructures, possibly filled with energetic material, into the mixture and the ignition with an electromagnetic pulse to produce volume combustion that improves efficiency and controls NOx pollution.
2. Description of the Related Art
Combustion drives the developed world's economy. Transportation is second only to industrial use as the largest consumer of energy in the US and accounts for about 60% of our nation's use of petroleum—an amount equivalent to all of the oil the country imports. The numbers are staggering: Some 10,000 gallons of petroleum are burned in the US each second of every day. Although new energy sources are being developed and renewable fuels are emerging to replace crude oil, improvements in the efficiency of internal combustion engines hold the promise of increasing our energy securing and mitigating climate change.
The environmental consequences and health hazards posed from urban smog and other combustion byproducts led to US regulation in the late 1970s designed to limited emission of nitrogen oxides (NOx), hydrocarbons, and other pollutants from internal combustion engines. Controlling those emissions while maintaining high efficiency is a continuing challenge. In the last decade, a combination of improved combustion technologies and exhaust after-treatments has nearly eliminated those emissions from gasoline spark-ignited engines. Emissions from the more efficient compression-ignited diesel engines have proven more difficult to control.
An internal combustion engine 10 is an engine in which the combustion of a fuel 12 occurs with an oxidizer 14 (usually air) in a combustion chamber 16. In an internal combustion engine the expansion of the high temperature and pressure gases, that are produced by the combustion, directly apply force to a movable component 18 of the engine, such as the pistons within a cylinder or turbine blades and by moving it over a distance, generate useful mechanical energy. The term internal combustion engine usually refers to an engine in which combustion is intermittent, such as the more familiar four-stroke and two-stroke piston engines, along with variants, such as the Wankel rotary engine. All internal combustion engines must achieve ignition in their cylinders to create combustion. Typically engines use either a spark ignition (SI) method 20 or a compression ignition (CI) system. In the past, other methods using hot tubes or flames have been used.
All internal combustion engines depend on the exothermic chemical process of combustion: the reaction of a fuel, typically with oxygen from the air—although other oxidizers such as nitrous oxide may be employed. The combustion process typically results in the production of a great quantity of heat, as well as the production of steam and carbon dioxide and other chemicals at very high temperature; the temperature reached is determined by the chemical make up of the fuel and oxidizers. The most common modern fuels are made up of hydrocarbons and are derived mostly from fossil fuels (petroleum). Fossil fuels include diesel fuel, gasoline and petroleum gas, and the rarer use of propane. Except for the fuel delivery components, most internal combustion engines that are designed for gasoline use can run on natural gas or liquefied petroleum gases without major modifications. Large diesels can run with air mixed with gases and a pilot diesel fuel ignition injection. Liquid and gaseous biofuels, such as ethanol and biodiesel (a form of diesel fuel that is produced from crops that yield triglycerides such as soybean oil), can also be used. Some engines with appropriate modifications can also run on hydrogen gas. Combustion or burning is a complex sequence of exothermic chemical reactions between a fuel (usually a hydrocarbon) and an oxidant accompanied by the production of heat or both heat and light in the form of either a glow or flames, appearance of light flickering. In a complete combustion reaction, a compound reacts with an oxidizing element, such as oxygen and the products are compounds of each element in the fuel with the oxidizing element. For example:CH4+2O2→CO2+2H2OIn the large majority of the real world uses of combustion, the oxygen (O2) oxidant is obtained from the ambient air and the resultant flue gas from the combustion will contain nitrogen:CH4+2O2+7.52N2→CO2+2H2O+7.52N2+heatAs can be seen, when air is the source of the oxygen, nitrogen is by far the largest part of the resultant flue gas.
In reality, combustion processes are never perfect or complete. In flue gases from combustion of carbon (as in coal combustion) or carbon compounds (as in combustion of hydrocarbons, wood etc.) both unburned carbon (as soot) and carbon compounds (CO and others) will be present. Also, when air is the oxidant, some nitrogen can be oxidized to various nitrogen oxides (NOx).
The hot gases produced by the combustion occupy a far greater volume than the original fuel, thus creating an increase in pressure within the limited volume of the chamber. This pressure can be used to do work, for example, to move a piston on a crankshaft or a turbine disc in a gas turbine. The energy can also be used to produce thrust when directed out of a nozzle as in a rocket engine.
Air-fuel ratio (AFR) is the mass ratio of air to fuel present during combustion. When all the fuel is combined with all the free oxygen, typically within a vehicle's combustion chamber, the mixture is chemically balanced and this AFR is called the stoichiometric mixture. AFR is an important measure for anti-pollution and performance tuning reasons. For gasoline fuel, the stoichiometric air/fuel mixture is approximately 14.7 times the mass of air to fuel. Any mixture less than 14.7 to 1 is considered to be a rich mixture, any more than 14.7 to 1 is a lean mixture—given perfect (ideal) “test” fuel (gasoline consisting of solely n-heptane and iso-octane). Lean mixtures produce hotter combustion gases than does a stoichiometric mixture, so much so that pistons can melt as a result. Rich mixtures produces cooler combustion gases than does a stoichiometric mixture, primarily due to the excessive amount of carbon which oxidizes to form carbon monoxide, rather than carbon dioxide. The chemical reaction oxidizing carbon to form carbon monoxide releases significantly less heat than the similar reaction to form carbon dioxide. (Carbon monoxide retains significant potential chemical energy. It is itself a fuel whereas carbon dioxide is not.) Lean mixtures, when consumed in an internal combustion engine, produce less power than does the stoichiometric mixture. Similarly, rich mixtures return poorer fuel efficiency than the stoichiometric mixture. (The mixture for the best fuel efficiency is slightly different from the stoichiometric mixture.) The AFR for a stoichiometric mixture will depend on the particular fuel. Therefore, a “lean” mixture is one having an AFR greater than the AFR for the stoichiometric mixture.
Lean burn refers to the use of lean mixtures in an internal combustion engine. The air-fuel ratios can be as high as 65:1, so the mixture has considerably less fuel in comparison to the stoichiometric combustion ratio (14.7 for petrol for example). A lean burn mode is a way to reduce throttling losses. An engine in a typical vehicle is sized for providing the power desired for acceleration, but must operate well below that point in normal steady-speed operation. Ordinarily, the power is cut by partially closing a throttle. However, the extra work done in pumping air through the throttle reduces efficiency. If the fuel/air ratio is reduced, then lower power can be achieved with the throttle closer to fully open, and the efficiency during normal driving (below the maximum torque capability of the engine) can be higher. The engines designed for lean burning can employ higher compression ratios and thus provide better performance, efficient fuel use and low exhaust hydrocarbon emissions than those found in conventional petrol engines. Ultra lean mixtures with very high air-fuel ratios can only be achieved by Direct Injection engines. The main drawback of lean burning is the large amount of NOx being generated at relatively high air/fuel ratios (i.e. greater than stoichiometric but less than 30:1).
If the mixture is too lean, the flame front produced by the spark plug will burn out and some of the fuel will not be burned. This reduces efficiency and increases pollutants.
To address this problem attempts have been made to replace the single-point spark plug ignition with a microwave source. The idea being that the microwave pulse will ignite fuel/air mixture throughout the volume thereby creating volume combustion. To date these efforts have not produced results significantly better than the conventional spark plug. See U.S. Pat. No. 4,064,852 “Microwave energy apparatus and method for internal combustion engines”, WO 99/37911 “Ignitiona nd Combution Support Device Using Microwave Technology For A Gasoline Engine”, WO 2005/059356 “Method for Igniting Combustion of Fuel in a Combustion Chamber of an Engine, Associated Device and Engine, and WO 2007/030782 “Microwave Combustion System for Internal Combustion Engines”, each of which are hereby incorporated by reference.